Zhang et al. / J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2019 20(7):563-575 563 Journal of Zhejiang University-SCIENCE B (Biomedicine & Biotechnology) ISSN 1673-1581 (Print); ISSN 1862-1783 (Online) www.jzus.zju.edu.cn; www.springerlink.com E-mail: [email protected] Comparison of volatile profiles and bioactive components of sun-dried Pu-erh tea leaves from ancient tea plants on Bulang Mountain measured by GC-MS and HPLC# Wen-jie ZHANG§1,2, Cong LIU§1,2, Rui-juan YANG1,2, Ting-ting ZHENG1,2, Miao-miao ZHAO1,2, Li MA1,2, Liang YAN†‡1,2 1College of Tea (Pu’er), West Yunnan University of Applied Sciences, Pu’er 665000, China 2Pu’er Institute of Pu-erh Tea, Pu’er 665000, China †E-mail: [email protected] Received Mar. 27, 2018; Revision accepted June 17, 2018; Crosschecked May 31, 2019 Abstract: To explore the volatile profiles and the contents of ten bioactive components (polyphenols and caffeine) of sun-dried Pu-erh tea leaves from ancient tea plants on Bulang Mountain, 17 samples of three tea varieties were an- alyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and high-performance liquid chromatography (HPLC). A total of 75 volatile components were tentatively identified. Laomaner (LME), Laobanzhang (LBZ), and other teas on Bulang Mountain (BL) contained 70, 53, and 71 volatile compounds, respectively. Among the volatile compounds, alcohols (30.2%–45.8%), hydrocarbons (13.7%–17.5%), and ketones (12.4%–23.4%) were qualitatively the most dominant volatile compounds in the different tea varieties. The average content of polyphenol was highest in LME (102.1 mg/g), followed by BL (98.7 mg/g) and LBZ (88.0 mg/g), while caffeine showed the opposite trend, 27.3 mg/g in LME, 33.5 mg/g in BL, and 38.1 mg/g in LBZ. Principal com- ponent analysis applied to both the volatile compounds and ten bioactive components showed a poor separation of samples according to varieties, while partial least squares-discriminant analysis (PLS-DA) showed satisfactory dis- crimination. Thirty-four volatile components and five bioactive compounds were selected as major discriminators (variable importance in projection (VIP) >1) among the tea varieties. These results suggest that chromatographic data combined with multivariate analysis could provide a useful technique to characterize and distinguish the sun-dried Pu-erh tea leaves from ancient tea varieties on Bulang Mountain. Key words: Sun-dried Pu-erh tea; Ancient tea plant; Bulang Mountain; Volatile compound; Bioactive component https://doi.org/10.1631/jzus.B1800183 CLC number: S571.1 1 Introduction Province, China, near the Chinese–Burmese border. Bulang Mountain, with an area of 1016.34 km2, is a Bulang Mountain is located in Menghai County, famous Pu-erh tea-producing area and is one of the Xishuangbanna Dai Autonomous Prefecture, Yunnan best preserved areas of ancient tea plants. There are 600 ha of gardens containing the Laomaner (LME), Laobanzhang (LBZ), and other ancient tea plants (BL) ‡ Corresponding author of the area. The tea plants are distributed mainly at § The two authors contributed equally to this work # Electronic supplementary materials: The online version of this article altitudes of 1300–1900 m (Tao et al., 2013). The teas (https://doi.org/10.1631/jzus.B1800183) contains supplementary mate- in Bulang Mountain are characterized by their unique rials, which are available to authorized users aroma, similar to the sweet smell of malt sugar. They ORCID: Liang YAN, https://orcid.org/0000-0003-4339-2684 © Zhejiang University and Springer-Verlag GmbH Germany, part of are yellow or green and have an immediate sweet taste Springer Nature 2019 followed by mellow and bitter tastes. They are very 564 Zhang et al. / J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2019 20(7):563-575 astringent (Xia et al., 2012). The plant stems are analysis (PCA) and partial least squares-discriminant strong and bear numerous hairs. As a valuable re- analysis (PLS-DA) were used to investigate the rela- source, the ancient teas in Bulang Mountain have tionships between the samples. To our knowledge, no been consistently pursued by tea traders and Pu-erh similar publications are available in the literature. tea enthusiasts worldwide. Food flavor mainly includes taste and aroma. Non-volatile compounds usually contribute to taste, 2 Materials and methods while volatile components contribute to aroma (Lin 2.1 Samples and chemicals et al., 2012; Du et al., 2014). The volatile components of sun-dried Pu-erh tea leaves from ancient tea plants Seventeen sun-dried Pu-erh tea samples belong are similar to those of common Pu-erh green or to three tea varieties, including five LME, six LBZ, Pu-erh raw tea leaves and include mainly alcohols, and six BL samples (Table 1), which were identified hydrocarbons, aldehydes, ketones, and esters (Lv et al., by the Pu’er Institute of Pu-erh tea (Pu’er, Yunnan, 2015). However, the relative volatile composition, China). Those samples were harvested in 2017 and concentrations, and perception thresholds of individ- kept in a dry environment. The samples were ground to ual components give sun-dried Pu-erh tea leaves of pass through a 30–60 mesh and sealed before use. these ancient tea plants their distinctive aroma. The Sodium chloride (99.5%, chromatographic grade, analysis of the volatile components of Pu-erh green the same below), linalool (98.0%), α-terpineol (98.0%), teas has been used for various purposes including geraniol (99.0%), nerol (99.0%), α-ionone (92.0%), distinguishing between teas from different mountains β-ionone (97.0%), (E)-nerolidol (≥85.0%), methyl salic- (Wu et al., 2016) and differentiating between varieties ylate (98.0%), and phytol (95.0%) were purchased from and quality grades (Lv et al., 2015). The non-volatile Sigma-Aldrich (St. Louis, MO, USA). A homologous components of the tea leaves include polyphenols, series of n-alkanes solutions (C8‒C32) was purchased alkaloids, polysaccharides, free amino acids, and from AccuStandard (USA) and used to calculate the proteins. Among these, polyphenol and alkaloid bio- retention index (RI) of each compound. Gallic acid, active components have been well studied, including (+)-catechin, (−)-gallocatechin, (−)-catechin gallate, gallic acid, (+)-catechin, (−)-gallocatechin, (−)-catechin (−)-epigallocatechin, (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, (−)-epicatechin gallate, gallate, (−)-epigallocatechin gallate, (−)-gallocatechin (−)-epicatechin, (−)-epigallocatechin gallate, caffeine, gallate, and caffeine were purchased from the Insti- and (−)-gallocatechin gallate (Fan et al., 2017). Up to tute for the Control of Pharmaceutical and Biological date, scientific information on volatile constituents, Products (Beijing, China). The purity of all these polyphenols, and alkaloids of different varieties of standards was above 95%. Acetonitrile, methanol, Pu-erh tea from ancient tea plants on Bulang Moun- and phosphoric acid (HPLC grade) were purchased tain is rather scarce (Cai et al., 2014). Therefore, an from Macklin (Shanghai, China). Ultra-pure water in-depth study is necessary to explore their volatile was obtained from a Milli-Q purification system profiles and bioactive component characteristics. (Millipore, Bedford, USA). The aim of this work was to chemically charac- 2.2 HS-SPME of samples terize the volatile components and ten bioactive components of Pu-erh tea leaves from ancient tea SPME is an equilibrium technique. Many ex- plants on Bulang Mountain using headspace-solid perimental parameters affect this equilibrium. To phase microextraction-gas chromatography-mass spec- ensure good-quality SPME extraction, optimization trometry (HS-SPME-GC-MS) and high-performance was needed (He et al., 2016). In this study, the effects liquid chromatography (HPLC). Principal component of major factors, such as extraction fiber, extraction Table 1 Information about sun-dried Pu-e rh tea leaves from ancient tea plants Sample ID Name Region Harvest time LME1–LME5 Laomaner tea Bulang Mountain Apr. 2017 LBZ1–LBZ6 Laobanzhang tea Bulang Mountain Apr. 2017 BL1–BL6 Other sun-dried Pu-erh tea of ancient tea plants Bulang Mountain Apr. 2017 Zhang et al. / J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2019 20(7):563-575 565 temperature, extraction time, and the amount of water, ards where available. The RIs of target components on extraction efficiency were investigated compre- were obtained using n-alkanes (C8–C32) under the hensively before the experiment. Through compari- same GC-MS procedure. The calculated RI was son of the total peak area, the optimal extraction compared with the reported RI. The percentage process was as follows: 4.0 g of tea sample was amount of target compound was calculated by the transferred into a 100-mL SPME headspace vial, percentage of peak area of target compound relative following the addition of 4.0 g of sodium chloride and to the total peak area of all compounds. 16 mL of water, and then the vial was sealed using a 2.4 Polyphenols and alkaloids analyzed by HPLC polytetrafluoroethylene (PTFA) septum. The vial was then placed on a magnetic stirring apparatus at 300 r/min The HPLC analysis was based on a slightly and equilibrated at 60 °C for 5 min. A 65-µm poly- modified method described by Wang et al. (2016a). dimethylsiloxane (PDMS)/divinylbenzene (DVB) fiber Each sample (about 0.2 g) was placed into a 10-mL (Supelco Inc., Bellefonte, USA) was exposed to the centrifuge tube, and 4 mL of preheated 70% methanol headspace over the sample for 60 min. After extrac- was added. The sample was extracted for 10 min in a tion, the fiber was exposed in the GC-MS injector at 70 °C water bath, and then the extract was centrifuged 250 °C for 4 min and then the headspace was imme- at 3500 r/min for 10 min. The supernatant was trans- diately analyzed by GC-MS.